KYIV -- President Petro Poroshenko has urged Ukrainians to mend their differences, saying that only unity can keep the country from descending into chaos in the face of what he called a persistent Russian military threat.

In an annual address to parliament, Poroshenko said that Moscow was trying to use the conflict in eastern Ukraine to "destroy us from within." He also warned that a full-scale Russian invasion could not be ruled out.

"At a time when Russia’s aggression against Ukraine is still ongoing, when the military threat from the east is the most difficult strategic challenge, the issue of national unity and political consolidation is a matter of life and death for our country," Poroshenko said in the televised speech on September 6, the opening day of the Verkhovna Rada's new session.

"The parliament is made up of the ruling faction and the opposition. This is an inviolable and important feature of democracy," he told the Verkhovna Rada. "But sometimes there are moments when you want to forget for a moment if you're right or left, liberal or conservative, a Ukrainian or Russian speaker."

Ukraine has been riven by war in the east, where Russia-backed separatists seized parts of two provinces after the Euromaidan protests brought down Moscow-aligned President Viktor Yanukovych in February 2014. Unity has also been undermined by disputes over legislation on language and communist symbols.

Poroshenko painted a hopeful portrait of a nation with an army that has grown stronger over the course of the war against the Russia-backed separatists, which has killed more than 9,500 people, but one that must be prepared to fight on its own.

Poroshenko thanked Ukraine's Western partners for their military support, which he claimed totaled more than half a billion dollars, but he said the country needed more help to defend its sovereignty. "Russian expansionism is a continental and global problem. It cannot be solved between two countries," he said. "Ukraine needs consistent international support to tackle Russian aggression."

But Poroshenko said that "securing this support is becoming increasingly difficult for our diplomats due to different objective and subjective factors."

He said that Europe was facing challenges from the migration crisis and militant attacks, and warned that elections in EU member states in 2017 could usher in political forces that are more willing to compromise with Russia.

Poroshenko painted a hopeful portrait of a nation with an army that has grown stronger over the course of the war against the Russia-backed separatists.

Warning that a full-scale Russian invasion cannot be ruled out, Poroshenko said he was prepared to appeal again for lethal defensive weapons from the West. But for now, he said, Ukraine "must rely most of all on itself."

But that could prove challenging, as Ukraine cannot afford to spend more than 3 percent of its gross domestic product on the military, he said, adding that the burden on the budget was "high enough" as it is. The army still needed support from volunteers, he said.

Poroshenko underlined what he said was Ukraine's desire to join NATO. "Our strategic goal is NATO membership," he said. "This road map is as immutable as the North Star in the starry sky."

Russia vocally opposes Ukrainian membership in NATO.

After warning about the possibility of imposing martial law last month amid an escalation of violence in eastern Ukraine, Poroshenko said he does not want martial law or a new mobilization for combat in the east. But he said the key to those issues "rests in Moscow," suggesting he would not rule out such measures if provoked by Russia.

A peace process based on 2014 and 2015 deals known as the Minsk accords has failed to end the fighting, and little progress has been made on the political aspects of the agreements.

Poroshenko said that Ukraine cannot afford to make concessions to Moscow, which says the first step should be for Kyiv to pass legislation giving the separatist-held territories more autonomy and granting the separatist fighters amnesty.

"Security issues remain first," Poroshenko said. "We must see a complete and sustainable cease-fire, the pull-out of Russian troops and military hardware, disarming of militants, control over the whole Ukraine-Russian border [returned to Kyiv]."

"Russia wants to turn the territory it occupies in the Donetsk and Luhansk regions, as someone has said, into a Donbas protectorate, and then infiltrate it back into Ukraine on its terms to destroy us from within," he said. "I'll put it bluntly, we will not allow them to do this and it will not happen."

Poroshenko also voiced hope for a much-anticipated European Union resolution on visa liberalization for Ukraine, saying its approval would be "proof that Europe is a key partner that recognizes our progress in implementing reforms."

EU Enlargement Commissioner Johannes Hahn expressed confidence on September 3 that there will be a decision in both the European Parliament and among EU member states to grant visa liberalization -- which would enable Ukrainians to travel more freely throughout the EU -- later this year.

Western leaders have criticized Kyiv over the pace of reforms and challenged it to do more. Both EU visa liberalization and another tranche of financial aid from the International Monetary Fund (IMF) are dependent on Ukraine making progress on reforms including steps to curb official corruption, which Poroshenko said was particularly crucial.

"We must demonstrate to the people that the battle against corruption has started at the top. Only then will we be able to tackle it at every level," he said.

With reporting by Reuters

Christopher Miller

Christopher Miller is a correspondent based in Kyiv and covers the former Soviet republics. He can be reached at millerjchristopher@gmail.com